I'm sticking with Sony for a few reasons.
1) Sony has never failed in this industry. The backed up the incredible Playstation with an even better PS2, plus their portable blows Nintendo's Gameboy out of the water. So the pretty much know what they are doing.
2) I'm really disappointed with the amount/type of games released exclusively on X-box. I mean, there's obviously titles that are on multiple platforms. But the one's that are exclusive to X-box, aren't that great. Even Halo, which may have great multi-player, is a dumb, shooter with no need for thought.
3) To build on the last point, Sony draws the most developers. They want to develop games for Sony, probably because the source code is easier to deal with. In any event, there are more types of games to choose from, and for the most part, they are all pretty good.
4) Since SNES, Nintendo has just plain sucked. Yes, the N64 was a breakthrough console, but the games absoultely sucked. They prolly made 10 different types of games starring Mario and his crew. The sports games were horrible, and there wasn't anything remotely interesting. GoldenEye was the exception. Then they followed up with GameCube, which sucked even more. What a waste of money. I grew up on Nintendo, but I can't trust them anymore.
5) Sony's console comes out later than Microsoft, which means, conceivable, Sony can make modifications based upon what the X-box 360 brings to the table.
Sony all the way.